Redox amplification processes have been described, for example in British Specification Nos. 1,268,126, 1,399,481, 1,403,418 and 1,560,572. In such processes color materials are developed to produce a silver image (which may contain only small amounts of silver) and then treated with a redox amplifying solution (or a combined developer-amplifier) to form a dye image.
The developer-amplifier solution contains a color developing agent and an oxidizing agent that will oxidize the color developing agent in the presence of the silver image which acts as a catalyst. An amplifier solution contains the oxidant but for its dye image forming depends on color developer carried over from the previous developer bath.
Oxidized color developer reacts with a color coupler to form the image dye. The amount of dye formed depends on the time of treatment or the availability of color coupler and is less dependent on the amount of silver in the image as is the case in conventional color development processes.
The stability of amplifier and developer/amplifier solutions is not good while that of bleach solutions can cause problems, though not to the same extent.
A number of ways of stabilizing amplifier and developer/amplifier solutions have been proposed in the art.
We have now found that the stability of a replenished amplifier, developer/amplifier, or bleach bath deteriorates as processing progresses (or as the solution is seasoned). It has now been discovered that this instability is apparently caused by silver deposited in the tank and pipework or other metallic parts of the machine. The present invention seeks to solve this problem.